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docs: Update networking details in the architecture doc

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Updated the doc to clarify certain networking details and
external links to some of the networking terms used.

Fixes #3308

Signed-off-by: Archana Shinde <archana.m.shinde@intel.com>
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Archana Shinde 2022-01-25 17:04:27 +05:30
parent 7d1a956471
commit 75ae536196
1 changed files with 20 additions and 19 deletions
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39
docs/design/architecture/networking.md
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@ -1,36 +1,37 @@
# Networking
See the [networking document](networking.md).
Containers will typically live in their own, possibly shared, networking namespace.
Containers typically live in their own, possibly shared, networking namespace.
At some point in a container lifecycle, container engines will set up that namespace
to add the container to a network which is isolated from the host network, but
which is shared between containers
to add the container to a network which is isolated from the host network.
In order to do so, container engines will usually add one end of a virtual
ethernet (`veth`) pair into the container networking namespace. The other end of
the `veth` pair is added to the host networking namespace.
In order to setup the network for a container, container engines call into a
networking plugin. The network plugin will usually create a virtual
ethernet (`veth`) pair adding one end of the `veth` pair into the container
networking namespace, while the other end of the `veth` pair is added to the
host networking namespace.
This is a very namespace-centric approach as many hypervisors or VM
Managers (VMMs) such as `virt-manager` cannot handle `veth`
interfaces. Typically, `TAP` interfaces are created for VM
connectivity.
interfaces. Typically, [`TAP`](https://www.kernel.org/doc/Documentation/networking/tuntap.txt)
interfaces are created for VM connectivity.
To overcome incompatibility between typical container engines expectations
and virtual machines, Kata Containers networking transparently connects `veth`
interfaces with `TAP` ones using Traffic Control:
interfaces with `TAP` ones using [Traffic Control](https://man7.org/linux/man-pages/man8/tc.8.html):
![Kata Containers networking](../arch-images/network.png)
With a TC filter in place, a redirection is created between the container network and the
virtual machine. As an example, the CNI may create a device, `eth0`, in the container's network
namespace, which is a VETH device. Kata Containers will create a tap device for the VM, `tap0_kata`,
and setup a TC redirection filter to mirror traffic from `eth0`'s ingress to `tap0_kata`'s egress,
and a second to mirror traffic from `tap0_kata`'s ingress to `eth0`'s egress.
With a TC filter rules in place, a redirection is created between the container network
and the virtual machine. As an example, the network plugin may place a device,
`eth0`, in the container's network namespace, which is one end of a VETH device.
Kata Containers will create a tap device for the VM, `tap0_kata`,
and setup a TC redirection filter to redirect traffic from `eth0`'s ingress to `tap0_kata`'s egress,
and a second TC filter to redirect traffic from `tap0_kata`'s ingress to `eth0`'s egress.
Kata Containers maintains support for MACVTAP, which was an earlier implementation used in Kata. TC-filter
is the default because it allows for simpler configuration, better CNI plugin compatibility, and performance
on par with MACVTAP.
Kata Containers maintains support for MACVTAP, which was an earlier implementation used in Kata.
With this method, Kata created a MACVTAP device to connect directly to the `eth0` device.
TC-filter is the default because it allows for simpler configuration, better CNI plugin
compatibility, and performance on par with MACVTAP.
Kata Containers has deprecated support for bridge due to lacking performance relative to TC-filter and MACVTAP.